Abstract

The industrial revolution marked the beginning of unprecedented anthropogenic growth and technological advancement that also inadvertently led to acute environmental degradation. This technological advancement was driven by the use fossil fuels such as crude oil. Crude oil extraction through drilling has resulted in widespread environmental pollution and deterioration of natural habitats. The Ondo State region in Nigeria presents one such expanse where large scale crude extraction operations have caused hazardous environmental pollution and toxic substance contamination. This study is a comprehensive and holistic study of the terrestrial soil ecosystem aimed towards elucidating the potential ecotoxicity that may have adversely affected the area. The results indicated that the terrestrial soil ecosystem was largely acidic (~pH6) and the organic matter content ranged from 6% to 12% indicating the soil was hydric. The results also indicated that the terrestrial soil environment was contaminated with toxic heavy metals including cadmium (Cd), chromium (Cr), lead (Pb) and arsenic (As). The toxic heavy metal concentration of the soil ecosystem was higher during the dry season. The Cr concentration in the soil samples was >3 ppm in most of the sampling sites, which exceeded WHO maximum permissible limit. Mean concentrations of the heavy metals in the soil samples in both seasons were of the order: Cr > Pb > Cd > As. The soil ecosystem was also characterized by a diverse and large population of microorganisms including bacteria like Enterobacter, Escherichia coli, and several species of fungi.

Keywords

Anthropogenic Growth;

Crude Oil Extraction;

Ecotoxicity;

Toxic Heavy Metals;

Ilaje.

Introduction

Over the past several decades, uncontrolled anthropogenic growth has led to overutilization and exploitation of natural resources as well as widespread environmental pollution and degradation. One of the more significant damaging effects of this unrestrained growth has been the uncontrolled assembly of excess waste materials, which is contaminated with a wide range of noxious substances as well as toxic heavy metals and various detrimental materials [1] [2] [3]. Reckless discharge practices for such waste products added an additional environmental burden to natural ecosystems and had resulted in hazardous consequences [4] [5]. This waste disposal has mostly affected terrestrial soil ecosystems, turning the useful soil systems into wastelands [6]. According to a report published by the United Nations Environment Program [7] on the Environmental Assessment of Ogoniland, such soil contamination not only affects the socio-economic life of the inhabitants of the affected region but also it has an adverse effect on the drinking water quality. Therefore, regulation and reversal of this colossal degradation of natural ecosystems necessitate an appropriate socioeconomic valuation of natural resources, along with an efficient and sustainable utilization of these natural resources and employment of responsible waste treatment technologies [8].

The extraction of crude oil and natural gases has had hazardous consequences on natural environments. Kvenvolden and Cooper [9] reported that crude-oil seepage is about 600,000 metric tons per year. Crude oil extraction through drilling in terrestrial, marine or coastal environments has been a source of significant concern. This drilling often leads to industrial accidents such as spillage and acute environmental degradation due to irresponsible waste expulsion practices.

This study has focused on the terrestrial soil ecosystem of the Ondo state region in Nigeria. This region is a major site for offshore and mainland crude oil drilling operations that are carried out by several multinational oil corporations [10]. Furthermore, due to the lack of adequate wastewater treatment facilities in the region, a substantial amount of the wastewater produced in the region flows through the network of rivers into the area under investigation and frequently contaminates the surrounding natural environment [11].

Soil samples were collected and studied to examine the nature and degree of potential environmental pollution in the natural environment of the region. To this end, several standard soil quality parameters, as well as physicochemical parameters, were analyzed in samples that were collected from several different sampling regions. Toxic heavy metals are generally defined as metals or metalloids that have relatively high density, occur in multiple oxidation states, and cause extreme toxic effects on living organisms even upon exposure to low concentrations [12] [13]. The toxic heavy metals are found either naturally in a given area or can accumulate in the region as a result of anthropogenic activities. They have the ability to interact and bind to cellular components and can inhibit metabolic functions and activities of living cells [14].

There have been several studies which sought to determine the extent and causes of toxic heavy metal distribution in various parts of the world [15] [16] [17] [18]. The results of Manta, Angelone, Bellanca, Neri and Sprovieri [15] demonstrated that in parts of Italy, the source of Pb, Zn, and Hg in topsoil could be traced to anthropogenic pollution, while other metals like Mn and Ni among were thought to be primarily naturally occurring metals. Lin, Teng and Chang [16] demonstrated that in Taiwan, urbanization and industrialization had led to the contamination of natural soil environments with toxic heavy metals. Arora et al. [18] , demonstrated that in parts of India, use of irrigation water contaminated with toxic heavy metals led to bio-accumulation within vegetables that were being consumed by the general population. Li, Ma, van der Kuijp, Yuan and Huang [17] summarized that mining activities and irresponsible mining waste discharge practices across several provinces of China led to toxic heavy metal pollution in the region.

Microorganisms are the keystone of any natural ecosystem as they regulate vital nutrient cycles in a natural environment and hence the microbial population dynamics of the terrestrial soil environment were also analyzed. Therefore, this study presents a comprehensive picture of the terrestrial soil ecosystem and reveals several facets of the natural environment that can lead to widespread pollution and environmental degradation with devastatingly hazardous consequences.